December 28, 2024, 02:50:56 AM
Forum Rules: Read This Before Posting


« previous next »
Pages: [1]   Go Down

Topic: GLC  (Read 11383 times)

0 Members and 1 Guest are viewing this topic.

Offline sdekivit

  • Chemist
  • Full Member
  • *
  • Posts: 403
  • Mole Snacks: +32/-3
  • Gender: Male
  • B.Sc Biomedical Sciences, Utrecht University
GLC
« on: October 22, 2005, 01:01:56 PM »
hey,

i have a question about GLC cause i have to analyse the fatty acid composition of phospholipids. The way i want to analyse this is to compare with an external standard, a mixture with fatty acids ranging from a chain of 12 C to 18 C . To do this' i'll make methylesters from the fatty acids.

Now i have to chose a type of column but i'm kinda lost. They said to me i should chose a polar stationary phase. But i have apolar compounds with a different chainlength. All are methylesters so the type of the polar group is unchanged, so i should separate on the basis of a different chainlength. That's why i thought of a apolar stationary phase.

Why do i need a polar stationary phase ? is it because the compund would be too much in the statiuonary apolar phase ?

(my reasoning is based on the fact that apolar compounds are attracted to apolar phases)
Logged

Offline Dude

  • Chemist
  • Full Member
  • *
  • Posts: 237
  • Mole Snacks: +42/-9
  • I'm a mole!
Re:GLC
« Reply #1 on: October 23, 2005, 05:24:59 PM »
Fatty acids tend to elute as broad tailing peaks on non-polar columns (ie DB-1 or siloxane type columns) so they are typically esterified (and hence made more non-polar) to make the peaks sharper.  A broad tailing peak is difficult to integrate (poor quantification).  You can buy an FFAP (I believe it stands for free fatty acid phase) column from Agilent and do the analysis directly (no esterification required) up to about C22 or so.
Logged

Offline Mitch

  • General Chemist
  • Administrator
  • Sr. Member
  • *
  • Posts: 5298
  • Mole Snacks: +376/-3
  • Gender: Male
  • "I bring you peace." -Mr. Burns
    • Chemistry Blog
Re:GLC
« Reply #2 on: October 23, 2005, 05:29:28 PM »
What is GLC?
Logged
Most Common Suggestions I Make on the Forums.
1. Start by writing a balanced chemical equation.
2. Don't confuse thermodynamic stability with chemical reactivity.
3. Forum Supports LaTex

Offline ATMyller

  • Chemist
  • Full Member
  • *
  • Posts: 223
  • Mole Snacks: +31/-6
Re:GLC
« Reply #3 on: October 24, 2005, 06:00:22 AM »
Quote from: Mitch on October 23, 2005, 05:29:28 PM
What is GLC?
Gas-liquid chromatography. Shame on you Mitch.
Logged
Chemists do it periodically on table.

Offline sdekivit

  • Chemist
  • Full Member
  • *
  • Posts: 403
  • Mole Snacks: +32/-3
  • Gender: Male
  • B.Sc Biomedical Sciences, Utrecht University
Re:GLC
« Reply #4 on: October 24, 2005, 11:09:11 AM »
Quote from: Dude on October 23, 2005, 05:24:59 PM
Fatty acids tend to elute as broad tailing peaks on non-polar columns (ie DB-1 or siloxane type columns) so they are typically esterified (and hence made more non-polar) to make the peaks sharper.  A broad tailing peak is difficult to integrate (poor quantification).  You can buy an FFAP (I believe it stands for free fatty acid phase) column from Agilent and do the analysis directly (no esterification required) up to about C22 or so.

ty :) and than in this polar stationary phase unsaturated fatty acids stay longer in the column because they can interact with the stationary phase  (pi-electrons) right ?
Logged

Offline Dude

  • Chemist
  • Full Member
  • *
  • Posts: 237
  • Mole Snacks: +42/-9
  • I'm a mole!
Re:GLC
« Reply #5 on: October 24, 2005, 01:51:35 PM »
That sounds reasonaible.  Empirically, I have noticed that oleic acid (C18 with one site of unsaturation) elutes later than stearic acid (C18 saturated) on this column.  I have not tested highly unsaturated samples.  On the less polar columns with polyethylene glycol stationary phases, the esterified acids elute with the more unsaturated materials coming out later.  This would be due to a greater amount of miscibility of the unsaturated acid derviatives (alkene is more polar than alkane) in the somewhat polar stationary phase.

As for the peak tailing, hydrogen bonding is likely the most dominant factor responsible for distorted fatty acid peaks on other columns (see McNair, HM; Miller, JM Basic Gas Chromatography, Wiley, 1998, p 60).
Logged

Offline movies

  • Organic Minion
  • Retired Staff
  • Sr. Member
  • *
  • Posts: 1973
  • Mole Snacks: +222/-21
  • Gender: Male
  • Better living through chemistry!
Re:GLC
« Reply #6 on: October 24, 2005, 02:19:06 PM »
Quote from: ATMyller on October 24, 2005, 06:00:22 AM
Gas-liquid chromatography. Shame on you Mitch.

Heh, you don't see it called GLC too much anymore.  It's usually just GC now.
Logged

Offline sdekivit

  • Chemist
  • Full Member
  • *
  • Posts: 403
  • Mole Snacks: +32/-3
  • Gender: Male
  • B.Sc Biomedical Sciences, Utrecht University
Re:GLC
« Reply #7 on: October 24, 2005, 04:00:56 PM »
true, but i prefer saying GLC and not GC because now i can see a liquid is used as a stationairy phase (althoug a solid stationairy phase, GSC, won't be used anymore these days)
Logged

waleed

  • Guest
Re: GLC
« Reply #8 on: May 28, 2006, 10:48:33 AM »
i have tried to seprate the fatty acid methyl esters using GCMS technique with a polar stantionary phase column" ODB" ,,, and it provide good results... so maybe i think u have to try this,,,  there u will find many procedures how to do this... about the external standerd whats the nomber of C atoms u used?
and as u know FAME is not high polar compounds .. so it can be easly separated in the Si phenyl alkyl stationary phase..

am wondering if u have a suitable procedure how to separte these phospholipids using HPLC with UV detection.. because i found many articles but non provided me good resluts,,,
thnx
Logged

Offline LynnC

  • New Member
  • **
  • Posts: 5
  • Mole Snacks: +1/-1
  • Gender: Female
Re: GLC
« Reply #9 on: May 30, 2006, 02:07:25 AM »
Hi. just want to give some suggestions regarding FAME analysis.
I have been running this test for quite sometime and found that column OMEGAWAX from Supelco is a good column for this.
does your analysis include determining trans fatty acid? if yes, this column will not be able to separate it out though.

Logged

Offline Mitch

  • General Chemist
  • Administrator
  • Sr. Member
  • *
  • Posts: 5298
  • Mole Snacks: +376/-3
  • Gender: Male
  • "I bring you peace." -Mr. Burns
    • Chemistry Blog
Re: GLC
« Reply #10 on: May 30, 2006, 03:19:01 AM »
Quote from: ATMyller on October 24, 2005, 06:00:22 AM
Quote from: Mitch on October 23, 2005, 05:29:28 PM
What is GLC?
Gas-liquid chromatography. Shame on you Mitch.
I use GSC so yeah I have no real excuse. ;P
Logged
Most Common Suggestions I Make on the Forums.
1. Start by writing a balanced chemical equation.
2. Don't confuse thermodynamic stability with chemical reactivity.
3. Forum Supports LaTex
Pages: [1]   Go Up
« previous next »
Sponsored Links